Just a hypothetical here. If Joe Biden was rumored (and there was some circumstantial evidence to indicate that it could possibly be true) to have murdered someone in Ukraine in order to protect his son's employers and thus his son's job would it then be improper to ask the government of Ukraine to investigate that even though Joe Biden were your political adversary?
Now of course Joe Biden didn't kill anyone (at least directly. It's hard to know if anyone died trying to defend themselves from a Russian AK with a box of MREs because they didn't get the weapons or any of the lethal aid that they begged the Obama administration for) but there is some evidence to suggest that Hunter Biden was given a very high paying managerial position (for which he hadn’t a shred of qualification) with a Ukrainian natural gas company solely to provide some political cover from corruption investigation as his father was then the Vice President of the United States who had control over if, when, and how much money would flow from the U.S. to Ukraine.
Is public corruption and bribery a crime anymore? Or are those only crimes relative to who happens to be in office at the time?
Is it unethical to investigate your political opponent for specific crimes possibly committed while in office? If the answer is maybe (depending on how serious the crime is) then how serious is serious enough? How far along the Jay Walking to Murder spectrum does that point lie? What will Joe Biden have to have done in order to warrant an investigation?
But that's just what an average guy thinks
